Support wr/wrr policy degradation

src/brpc/load_balancer.cpp

@@ -24,6 +24,11 @@
 namespace brpc {
 
 DEFINE_bool(show_lb_in_vars, false, "Describe LoadBalancers in vars");
+DEFINE_int32(default_weight_of_wlb, 0, "Default weight value of Weighted LoadBalancer(wlb). "
+             "wlb policy degradation is enabled when default_weight_of_wlb > 0 to avoid some "
+             "problems when user is using wlb but forgot to set the weights of some of their "
+             "downstream instances. Then these instances will be set default_weight_of_wlb as "
+             "their weights. wlb policy degradation is not enabled by default.");
 BRPC_VALIDATE_GFLAG(show_lb_in_vars, PassValidate);
 
 // For assigning unique names for lb.

src/brpc/load_balancer.h

@@ -108,6 +108,7 @@ class LoadBalancer : public NonConstDescribable, public Destroyable {
 };
 
 DECLARE_bool(show_lb_in_vars);
+DECLARE_int32(default_weight_of_wlb);
 
 // A intrusively shareable load balancer created from name.
 class SharedLoadBalancer : public SharedObject, public NonConstDescribable {

src/brpc/policy/weighted_randomized_load_balancer.cpp

@@ -35,18 +35,23 @@ bool WeightedRandomizedLoadBalancer::Add(Servers& bg, const ServerId& id) {
         bg.server_list.reserve(128);
     }
     uint32_t weight = 0;
-    if (butil::StringToUint(id.tag, &weight) &&
-        weight > 0) {
-        bool insert_server =
-                 bg.server_map.emplace(id.id, bg.server_list.size()).second;
-        if (insert_server) {
-            uint64_t current_weight_sum = bg.weight_sum + weight;
-            bg.server_list.emplace_back(id.id, weight, current_weight_sum);
-            bg.weight_sum = current_weight_sum;
-            return true;
+    if (!butil::StringToUint(id.tag, &weight) || weight <= 0) {
+        if (FLAGS_default_weight_of_wlb > 0) {
+            LOG(WARNING) << "Invalid weight is set: " << id.tag
+                         << ". Now, 'weight' has been set to 1 by default.";
+            weight = FLAGS_default_weight_of_wlb;
+        } else {
+            LOG(ERROR) << "Invalid weight is set: " << id.tag;
+            return false;
         }
-    } else {
-        LOG(ERROR) << "Invalid weight is set: " << id.tag;
+    }
+    bool insert_server =
+             bg.server_map.emplace(id.id, bg.server_list.size()).second;
+    if (insert_server) {
+        uint64_t current_weight_sum = bg.weight_sum + weight;
+        bg.server_list.emplace_back(id.id, weight, current_weight_sum);
+        bg.weight_sum = current_weight_sum;
+        return true;
     }
     return false;
 }

src/brpc/policy/weighted_round_robin_load_balancer.cpp

@@ -78,17 +78,22 @@ bool WeightedRoundRobinLoadBalancer::Add(Servers& bg, const ServerId& id) {
         bg.server_list.reserve(128);
     }
     uint32_t weight = 0;
-    if (butil::StringToUint(id.tag, &weight) &&
-        weight > 0) {
-        bool insert_server =
-                 bg.server_map.emplace(id.id, bg.server_list.size()).second;
-        if (insert_server) {
-            bg.server_list.emplace_back(id.id, weight);
-            bg.weight_sum += weight;
-            return true;
+    if (!butil::StringToUint(id.tag, &weight) || weight <= 0) {
+        if (FLAGS_default_weight_of_wlb > 0) {
+            LOG(WARNING) << "Invalid weight is set: " << id.tag
+                         << ". Now, 'weight' has been set to 1 by default.";
+            weight = FLAGS_default_weight_of_wlb;
+        } else {
+            LOG(ERROR) << "Invalid weight is set: " << id.tag;
+            return false;
         }
-    } else {
-        LOG(ERROR) << "Invalid weight is set: " << id.tag;
+    }
+    bool insert_server =
+             bg.server_map.emplace(id.id, bg.server_list.size()).second;
+    if (insert_server) {
+        bg.server_list.emplace_back(id.id, weight);
+        bg.weight_sum += weight;
+        return true;
     }
     return false;
 }